The present invention relates to an image forming apparatus, and, especially, to an image forming apparatus which is suitable for detecting an anomaly in an attachment state or in a shunt operation of a transfer device, which transfers a color image from an intermediate transfer device onto a record medium.
The conventional apparatuses, such as the apparatus disclosed in Japanese Patent Application Laid-Open Hei 11-237814, are composed of a photoconductor, a transfer device for transferring a toner image formed on the photoconductor onto a record medium, a power supply for applying a voltage to the transfer device, a current detector for detecting current flowing in the transfer means, a voltage-control means for controlling the voltage of the power supply based on the current detected by the current detector, and a determination means for determining the presence of the photoconductor based on the current detected by the current detector.
Although the above-disclosed conventional apparatus uses a technique which detects whether or not the photoconductor is actually attached in the color image forming apparatus, it cannot detect the presence of a transfer device which is moved to a shunt position during a period when a color image is being formed on an intermediate transfer device by superimposing toner images thereon, and is put in contact with the intermediate transfer device during a period when the color image on the intermediate transfer device is transferred by the transfer device onto a record medium. Further, it is impossible to detect an anomaly in the switching operation involving the movement of the transfer device to the shunt position and to the contact position with the intermediate transfer device.
Further, there has been a problem in which the reliability of detection of an anomaly in the movement of a transfer device is generally low, because the value of current flowing in the transfer device changes depending on temperature and humidity in the environment in which the image forming apparatus, including the transfer device, is located.
An object of the present invention is to provide an image forming apparatus which can detect an erroneous attachment of a transfer device, which is likely to occur at the time of replacement of the transfer device, during inspection and maintenance work, or which can detect an anomaly in the switching operation involving movement of the transfer device between the shunt position and the position in contact with the intermediate transfer device.
Also, another object of the present invention is to provide a color image forming apparatus which can detect an anomaly of a transfer device with high accuracy by preventing an erroneous anomaly-detection due to changes in conditions of the environment in which the image forming apparatus, including the transfer device, is located.
To achieve the above objects, the present invention provides an image forming apparatus comprising an image forming device on which toner images are formed; a transfer device for transferring the toner images onto a record medium; a voltage-application means for applying a transfer voltage to the transfer device; a current-detection means for detecting current flowing between the image forming device and the transfer device; a storage means for storing a first current value detected when the transfer device is at a non-operation position, and a second current value detected when the transfer device is at an operation position; and a state-determination means for determining the presence of the transfer device and an occurrence of an anomaly in the contact of the transfer device with the image forming device and in a shunt operation in which the transfer device is displaced from the image forming device.
The image forming apparatus further includes a photoconductor on which electrostatic latent images are formed, and a development device for developing the latent images; wherein the image forming device is an intermediate transfer device onto which the images developed on the photoconductor are transferred.
Also, in the image forming apparatus, the respective images formed on the photoconductor are developed with toners of different colors, and the images developed with the toners of different colors arc superimposed on the intermediate transfer device.
Furthermore, in the image forming apparatus, the transfer device is moved into contact with and is separated from the intermediate transfer device, and the first current value, which is detected when the transfer device is at a position spaced from the intermediate transfer device, is stored in the storage means.
Still further, in the image forming apparatus, the second current value, which is detected after a control command signal operates to move the transfer device into contact with the intermediate transfer device, is stored in the storage means, and the state-determination means determines the presence of the transfer device. The occurrence of an anomaly in the contact of the transfer device with the image forming device, and in the movement of the transfer device to a shunt position away from the image forming device, is detected based on the stored first and second current values.
In addition, in the image forming apparatus, the occurrence of anomaly is detected by the state-determination means by comparing a current difference between the first and second current values with a predetermined reference value.
Also, in the image forming apparatus, the respective first and second current values are detected multiple times, and an average of current difference values, obtained with these first and second current values, is used as the reference value.
Further, in the image forming apparatus, each current difference value, obtained at every determination executed by the state-determination means, which has been determined to be normal, is stored in the storage means, and the reference value is set or corrected using a statistic value, which is obtained by statistically processing the history of die stored current difference values.
Moreover, the present invention provides a color image-forming apparatus comprising a photoconductor on which electrostatic latent images are formed by charging and exposing the photoconductor, and on which toner images of the latent images are formed by developing the latent images; an intermediate transfer device, which partially contacts the photoconductor, for receiving a first transfer of each of the toner images on the photoconductor, for each color, on its surface while moving endlessly; a control means for forming a color image by causing the toner images of plural colors to be superimposed on the intermediate transfer device; a transfer device for performing a second transfer of the color image onto a record medium; a transfer device contact/shunt operations-switching mechanism for placing the transfer device in a non-contact state with respect to the intermediate transfer device by moving the transfer device to a predetermined shunt position away from the intermediate transfer device during a color image-forming period, and for causing the transfer device to be pressed against the intermediate transfer device via a record medium after the completion of color image-formation; a power-supply means for changing and applying a transfer voltage to the transfer device when the color image is transferred from the intermediate transfer device onto the record medium; a current-detection means for detecting current between the transfer device and the intermediate transfer device; a transfer voltage-setting means for setting up the transfer voltage based on the detected current; and a transfer state-determination means for determining the presence and attachment state of the transfer device, and the occurrence of an anomaly in the contact of the transfer device with the image forming device and in the movement of the transfer device from the image forming device to the shunt position, based on the stored first and second current values.
Further, in the color image-forming apparatus, a first current value is detected by the current-detection means when the transfer device is pressed on the intermediate transfer device without the intervention of a record medium during a non-transfer period of the transfer, and a second current value is detected by the current-detection means when the transfer device is in a non-contact state in which the transfer device is located at a predetermined position away from the intermediate transfer device.
Also, in the color image-forming apparatus, the state-detection means determines the presence and attachment state of the transfer device, and the occurrence of an anomaly in the contact of the transfer device with the image forming device and in the movement of the transfer device to a shunt position away from the image forming device, based on a current difference between the first and second current values.
To achieve the above object, the present invention also provides a method of determining an anomalous state of a transfer device in an image forming apparatus including an image forming device on which toner images are formed, a transfer device for transferring the toner images onto a record medium, a voltage-application means for applying a transfer voltage to the transfer device, a current-detection means for detecting current flowing between the image forming device and the transfer device, and a storage means for storing values of the detected current, the method comprising the steps of: applying a predetermined voltage to the transfer device after it is confirmed that a command signal for operating the image forming apparatus has been output; detecting a first current flowing between the transfer device and the image forming device at least one time; storing a value of the detected first current in the storage means; pressing the transfer device against the image forming device; detecting a second current flowing between the transfer device and the image forming device at least one time; storing a value of the detected second current in the storage means; calculating a difference between the values of the detected first current and second current; comparing the difference with a predetermined reference value; and determining that the transfer device is in an anomalous state, if the difference is smaller than the predetermined reference value.
Further, in the above method, the respective first and second current values are detected plural times, and an average of current difference values obtained with these first and second current values is used as the reference value.
Furthermore, in the above method, each current difference value obtained at every determination executed by the transfer device state-determination means, which has been determined to be normal, is stored in the storage means, and the reference value is set or corrected using a statistic value, which is obtained by statistically processing the history of the stored current difference values.